1. Field of the Invention
The present disclosure relates to semiconductor integrated circuits, and in particular to integrated circuits used in devices providing multiple purposes to end users, such as television, audio, Internet access, telephone service and the like.
2. Description of the Related Art
Increasingly, consumer products are being developed as multiple purpose devices. Examples include using mobile telephones to function as MP3 players, cameras & radios, using portable storage devices as media players and using television “set top boxes” as devices to access the Internet and provide telephone services. In such devices, the different purposes can be provided by different integrated circuits, or increasingly by multiple purpose integrated circuits.
Integrated circuits (computer chips) that support digital television often have extensive mechanisms for protecting encrypted data against viewing or distribution by or to devices that are not entitled to do so. These “conditional access” systems employ a significant amount of hardware to protect these systems against attack by persons wanting to view, distribute or sell systems that can circumvent security for third parties.
There are two conventional approaches to providing security in the boot phase of integrated circuits. In a first, simple approach, the integrated circuit itself stores all the boot code in internal memory. This on chip code is trusted and is then used to load and authenticate further code in external memory. The disadvantage of this approach is the need to store the boot code in internal memory which uses space on the circuit. In a second approach, the boot loader code is stored in the circuit as part of a cryptocore. The cryptocore is arranged to verify code stored in external memory before it is executed. The disadvantage of this approach is the need for significant hardware.